Drawout apparatus are well known expedients for facilitating the installation and removal of physically large electrical devices, such as switches and circuit breakers, with respect to switchboards and panelboards. The device is provided with plug-in or stab-type disconnect primary contacts which mate in electrical interconnection with complementary switchboard primary disconnect contacts incident to racking movement of the device to its innermost, engaged position, thereby making the electrical joints requisite to electrically connecting the device into the switchboard.
In higher current applications, the devices become quite large and heavy, thus rendering the bodily movement of the devices necessary to electrically connect and disconnect them from the switchboard extremely cumbersome without structure supporting the device in its racking movement. Moreover, as current ratings increase, the requisite high contact pressures embodied in the primary disconnect contacts become extremely difficult, if not impossible, to overcome without mechanical assistance. Thus, drawout apparatus for accommodating these larger electrical devices typically include not only provisions for supporting the device during racking movement, but also various camming or levering mechanisms operating to mechanically assist the racking movement of the device at least during that segment of travel necessary to engage and disengage the device-switchboard primary disconnect contacts.
The principle limitation to the utilization of drawout apparatus is the ability of the plug-in primary terminal joints to carry the increasingly higher currents called for in many applications. These joints are sources of heat which can contribute to an intolerable high temperature condition within the switchboard. The spring forces incorporated in such plug-in terminal connectors and their mutual contact surface areas, which will accommodate sliding relative movements of the mating connectors incident to making and breaking the plug-in joints, are not sufficient to achieve a cool running joint in high current applications. Consequently, bolted terminal joints must be resorted to, and, as a result, the signal advantage in drawout installations of being able to connect and disconnect a device from a live switchboard without having to operate directly on the primary terminal joint is lost.
It is accordingly an object of the present invention to provide improved drawout apparatus capable of racking electrical devices of large size and weight into and out of an electrical enclosure.
An additional object of the present invention is to provide an electrical switchboard having particular utility in high current applications and incorporating improved drawout apparatus of the above character.
A further object of the present invention is to provide drawout apparatus of the above character adapted to support an electrical device for racking movement between extended and engaged positions with respect to primary terminals of an electrical switchboard.
Yet another object of the present invention is to provide drawout apparatus of the above character which includes provisions for effecting cool running electrical joints between the device and switchboard primary terminals.
Still another object of the present invention is to provide an electrical switchboard of the above character, which is inexpensive to manufacture, efficient in design, rugged in construction, and safe and reliable in operation.
Other objects of the invention will in part be obvious and in part appear hereinafter.